1. Field of the Invention
The present invention relates to transcoding a first video data file to produce a second video data file for downloading that can be viewed progressively as the file is being downloaded.
2. Description of the Related Art
Methods for the transcoding of video data files to produce a new video data file in a different video format are known. It is also known to stream video data so that the data may be viewed progressively as it is being received at a mobile device for example. However, it is also known that some mobile devices are not configured to display streamed data but are equipped to display a file after it has been downloaded. It is therefore desirable to download a file to a device for later viewing while at the same time allowing the device to view the file progressively as it is being received. However, a problem exists when transcoding data of this type in that it is necessary to provide information identifying the size of a downloaded file. This creates a problem if the file is being transcoded on the fly because the total size of the resulting file will not be known until the resulting file has been completely transcoded.
Transcoding operations are regularly performed when video material held at a remote server is accessible over the Internet. However, the stored material is primarily configured for being displayed on static workstations or television receivers etc. A transcoding operation is therefore required if the material is to be displayed on a mobile device, such as a mobile telephone. Thus, it is necessary to identify the original coding parameters, identify the coding parameters required by a receiver and then perform a transcoding operation to convert from the original type of coding to the recipient's type of coding. If the recipient is looking to download a file (for viewing later) a delay will be incurred before the recipient is in a position to view the file. Thus, a preferred approach would be to stream the file so that the recipient can view the file while the data is being received, while at the same time retaining a downloaded version of the file. In this way, the download delay is not so noticeable.
Further delays occur during the transcoding process. Transcoding delays may be minimised by performing a technique of rapid transcoding as described in the present applicant's co-pending European Patent Application No 08 253 317.5 filed 10 Oct. 2008 or in the applicant's co-pending U.S. patent application Ser. No. 12/330,782 filed 9 Dec. 2008. However, such an approach does require dedicated hardware.
An alternative approach to rapid transcoding would be to perform the transcoding operation in a conventional serial fashion but to allow the video material to be sent to the recipient on the fly while the transcoding operation is being performed. In this way, assuming the recipient can view streamed material, both the transcoding delay and the download delay are avoided and the display of video at the recipient's equipment appears almost instantaneous. However, if in addition to viewing the material as a stream the data file is also downloaded, it is necessary for the receiving equipment to be made aware as to the total size of the downloaded file. Should this identification of size be incorrect, failures could occur at the recipient's equipment, possibly due to the equipment awaiting a data chunk that does not exist. However, if the transcoding process is still ongoing while material is being received, the transcoder would not be aware as to the total size of the file therefore it could not provide the recipient with file size information. A problem therefore exists in terms of providing a file as a stream, so that it may be viewed as the material is received, while at the same time making the file compatible with a downloaded file, so that the file may be viewed after it has been downloaded and stored.